Smoke agent



Patented Nov. 10, 1953 UNITED STATES TENT OFFICE SMOKE AGENT John P. Clay and Hervey B. Elkins, United States Army, assignors to the United States of America as represented by the Secretary of War 2 Claims.

(Granted under The invention described herein may be manufactured and used by or for the Government, for governmental purposes, without the payment to me of any royalty thereon.

This application is a division of our application for patent, Serial No. 562,328, now matured into U. S. Patent No. 2,574,466, issued November 13, 1.951.

This invention relates to a chemical agent filling for munitions and a process for preparing the agent. More particularly, this invention is concerned with a new smoke agent formulated principally with red phosphorus and with a plasticizer.

It has been recognized that by far the most efficient material used in warfare for generating artificial smoke is white phosphorus. Phosphorus exists in two allotropic forms: white phosphorus and red phosphorus. White phosphorus, the normal and common form, is a waxy white solid that is spontaneously inflammable at ordinary temperatures and burns with formation of a dense white smoke of highest obscuring power. Red phosphorus is produced by heating white phosphorm to a temperature of about 250- 300 C. out of contact with air. Red phosphorus is a reddish brown amorphous powder which is much less chemically active than white phosphorus. In contact with air at ordinary temperatures, red phosphorus remains unchanged for a long time; it does not dissolve in ordinary solvents for white phosphorus; it does not become luminous; and can be heated to 260 C. before it ignites. Red phosphorus vapors are not toxic as are the vapors of white phosphorus. Despite a number of advantages to be gained by using red phosphorus instead of white phosphorus in smoke munitions it was hitherto found impractical to use red phosphorus, although many years ago some attempts were made to use red phosphorus mixed with white phosphorus for generating smoke.

While white phosphorus acts efiiciently in many munitions, it is still subject to several drawbacks. Its storage and handling are difiicult and require special equipment, due to its spontaneous infiammability. Its melting point is below temperatures frequently reached in storage, and above this temperature many compositions of white phosphorus are unstable, the white phosphorus separating from other ingredients which under normal conditions are compatible. The requirement of thermal stability limits the preparation of white phosphorus compositions With other ingredients to a narrow litle 35, U. S. Code (1952),

see. 266) range of mixtures, with the result that burning and fragmentation characteristics of white phosphorus composition can not be suitably adjusted for all circumstances. In addition, white phosphorus munitions have certain limitations on their uses. White phosphorus produces a bright flame when burning; it leaves on wet terrain unburned residues which ignite spontaneously when uncovered or dry to form a hazard to friendly troops entering the area.

Accordingly, one of the main objects of this invention is to provide a red phosphorus containing agent comparable in smoke producing efiiciency to white phosphorus or compositions containing White phosphorus.

The further object of this invention is to provide a red phosphorus containing a smoke mixture highly suitable as a filling for various munitions such as bombs, grenades, rockets, and the like.

A further object is to provide a red phosphorus smoke agent filling capable of being readily ignited by standardized fuzings and of producing an effective smoke cloud of long duration with a minimum of pillaring.

An additional object or" this invention is to provide a plastic red phosphorus smoke agent which is stable over a wide range of temperatures, easily prepared, and readily loaded into standardized chemical munitions.

A still further object is to provide a red phosphorus smoke agent which has a number of tactical and training uses for which white phosphorus is not suitable.

Further and additional objects will appear from the following description and appended claims.

In accordance with this invention, an improved red phosphorus containing smoke agent useful as a munition filling is provided by mixing red phosphorus with a plasticizer, preferably with a plasticizer and a volatile, flammable liquid that is compatible with the plasticizer employed.

A wide variety of plasticizers can be used with red phosphorus such as natural rubber, synthetic rubber or elastomers, acrylate polymers, aluminum soaps of high molecular weight fatty acids, and, in general, high molecular weight organic polymers and organic materials which thicken or gel flammable organic liquids when added thereto in minor proportions.

Preferably, the plasticized red phosphorus mixture comprises a major proportion of red phosphorus and a minor proportion of the plasticizer, these ingredients being thoroughly incorporated, one with the other, to produce a relatively stiff, doughy, .or jelly-like mass which may be readily introduced into ordinary phosphorus munitions such as bombs, shells, grenades, rockets, and the like.

In order that the rubber or other plastic material may be readily incorporated with the red properly mixed is stable and does not tend to separate over a wide range of temperatures. The consistency of the filling composition is readily controlled by proper selection of the kind and amount of plasticizer. The burning rate of the mixture may likewise be controlled, the burning rate being slower generally with the use of more plasticizer. Also the consistency and burning rate may be varied by the addition .of various oxidizing agents, reducing agents, and inert materials. For example, oxidizing agents, such as, sodium nitrate, potassium nitrate, or barium nitrate, may be added to support combustion. Inert materials, such as, asbestos fibers, wood fibers, carbon, cotton waste, or other pa-rticulate material, may be added to change the consistency and decrease the burning rate. Finely divided pyrophoric metal and other combustible substances, such as asphalt, may be added to change burning characteristics.

No special equipment is necessary for proper mixing of the ingredients.

As an illustration of one embodiment of the invention and of the simplicity in preparing the plasticized red phosphorus agent, a solution of isobutylmethacrylate polymers in gasoline was mixed with red phosphorus powder simply by stirring these ingredients with a spatula in an open vessel. The resulting mixture was readily ignited with a match and produced a good screening smoke.

Another example of a satisfactory plastic ,filling prepared simply by mixing the ingredients is a mixture containing 75% red phosphorus, 2 rubber and 22 gasoline.

Mixtures which have been tested most widely contained synthetic rubber, particularly butadiene styrene copolymer rubber, known commonly as Buna-S, in a weight proportion of about 26% with about 26 to 30% gasoline and about 70 .to 75% red phosphorus. Tests were carried out by exploding these mixtures in munitions such as a grenade and a standardized 100 pound chemical bomb (M47). Bombs filled with the thus prepared plasticized red phosphorus agent were dropped from an airplane and the effects were compared with the efiects of 100 lb. bombs filled with white phosphorus and ,plasticized white phosphorus compositions. It was judged that the plasticized red phosphorus agent generated a superior screening smoke which lasted for a longer period than that generated by the other agents. The smoke from the plasticized red phosphorus agent did not pillar, whereas the white phosphorus filling in the burster type bomb pillared badly.

A mi tur s O red phos h r-us With 103. 1

phosphorus.

plasticizing agents and solvents were prepared and tested in various munitions with satisfactory results, the most satisfactory smoke being obtained when the mixtures comprised predominantly, i. e., more than 50% by weight, of red We have previously disclosed that we use up to of this incendiary ingredient and :hence it will be understood that our agent, by weight, may consist of from about 50% to about 75% of the red phosphorus.

In plasticizing red phosphorus, a number of flammable solvents or liquids may be used which cannot be .used suitably with white phosphorus.

addition to solvents which have been described, such liquids as acetone, ethyl acetate, carbon disulfide, and the like may be employed with appropriate plastics, thickeners, or gellingagents, preferably organic plastics of high heating value.

Red phosphorus is practically non-poisonous and can be safely handled. Plasticized red phosphorus mixtures containing no white phosphorus are also safe to handle, being stable and not being spontaneously inflammable. No special precaution nor special skill is necessary in preparing the plasticized red phosphorus mixtures.

Elasticized red phosphorus similar in jellylike consistency to gelled gasoline canbe used in munitions designed for such incendiary ,material with the same type of ignition mechanism, as .for example, tail ejection bombs, burster type bombs, and grenades.

On account of the simplicity with which the plasticized red phosphorus mixtures can be prepared, they may be prepared advantageously in the field. Although an effective smoke agent may be prepared also by mixing white phosphorus with red phosphorus and a plasticizer, there are certain difficulties in making this mixture due to the spontaneous infiammability of vwhite phosphorus and also the difi'iculty of mixing white and red phosphorus under water, since red phosphorus is dispersed readily in water employed in preparing the mixture.

There are additional advantages in the .uses of the plasticized red phosphorus filling over white phosphorus fillings, as for example, in munitions difiicult to make safe when filled with white phosphorus in any form, in tail ejection munitions which require a filling which has suitable consistency, and in large burster type munitions.

It will be apparent that the use of red phosphorus in a smoke agent comparable in effectiveness to white phosphorus is highly beneficial and remarkable considering the many difficulties in handling and use of white phosphorus and the futile efforts over many years to establish the use of red phosphorus in a smoke agent.

It is to be understood that other modifications in the preparation, composition, and use of the plasticized red phosphorus agent may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that this invention be limited only by the scope '5: the appended claims. 7

We claim:

1. A plastic chemical smoke producing filling for munitions consisting, by weight, essentialiy of a mixture of from about 50% to about 75 red phosphorus, from about 2% to about 6%isobutylmethacrylate polymers and a hydrocarbon solvent selected from the group consisting of gasoline .and xylene.

2. The filling of claim 1 in which the solvent is gasoline.

JOHN P. CLAY. HERVEY B. ELKINS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Thomas Feb. 3, 1920 Nichols June 13, 1922 10 White June 14, 1932 Vollrath Mar. 7, 1939 Clay et a1. Nov. 13, 1951 6 FOREIGN PATENTS Number Country Date 7,314 Great Britain of 1915 269,979 Great Britain Apr. 27, 1927 OTHER REFERENCES Fire from the Air, by Zanetti, 1942, pages 18-24.

Chemical Formulary, Bennett Chemical Publishing (30., N. Y., 1941, page 604.

Hackhs Chemical Dictionary, 1950, page 557. 

1. A PLASTIC CHEMICAL SMOKE PRODUCING FILLING FOR MUNITIONS CONSISTING, BY WEIGHT, ESSENTIALLY OF A MIXTURE OF FROM ABOUT 50% TO ABOUT 75% RED PHOSPHORUS, FROM ABOUT 2% TO ABOUT 6% ISOBUTYLMETHACRYLATE POLYMERS AND A HYDROCARBON SOLVENT SELECTED FROM THE GROUP CONSISTING OF GASOLINE AND XYLENE. 